WATER-PLANTS 43 
superabundant. In such places we are plea with a 
vegetation exhibiting a great number of species and 
a marked variety of form, and by no means so easy to 
correlate with its environment as those which we have 
been considering. In a wide sense, the nature of the 
vegetation is largely dependent on the degree of aera- 
tion of the water and the amount of dissolved mineral 
salts which it contains, an increase of either (within 
limits) resulting in a richer flora. But in any one 
CELE 
Ree he tee y liffii/ 
Wl NY 
Paice cd in 
fe A ba | mate all | 
ih 
a. Stall ‘ mg | 1 
ee ae 
pas. 
Fic. 6.—DIAGRAM ILLUSTRATING SUCCESSION OF VEGETATION 
IN LAKES. 
a, Marsh zone; J, reed zone; c, zone of floating vegetation ; 
d, zone of submerged vegetation. 
area it is clear that depth of water is the controlling 
factor: the plants are arranged in zones, one succeed- 
ing another as the bottom shelves. Two main zones 
are conspicuous: (1) A zone of tall reed-like plants 
near the margins, which farther out is succeeded by 
(2) a zone of lax floating plants which either have 
leaves resting on the surface or grow entirely sub- 
merged. Above the former a belt of marsh plants 
links the reed zone with the vegetation of the soils of 
normal moisture; below the latter, should the water 
